維摩經玄疏 2.38

2.38

此三通名觀者，「觀」以觀穿為義，亦是觀達為能。觀穿者，穿見思恒沙無明之惑，故名觀穿也。觀達者，達三諦之理也。故《大涅槃經》云「如人善知伏藏，即取利钁，掘地直下，槃石、沙、礫，直過無難，唯至金剛，不能穿徹」。槃石者，見思惑也。砂者，塵沙無知惑也。礫者，即是無明住地惑也。徹過者，即觀穿義也。至金剛者，即達一實諦佛性理也。

The reason these three are collectively called 'contemplations' is that 'contemplation' (guan) has the meaning of 'piercing through' (guanchuan) and also has the function of 'thoroughly penetrating' (guanda). 'Piercing through' means piercing through the delusions of views and thoughts, of [delusions as numerous as] the Ganges sands, and of fundamental ignorance; hence it is called 'piercing through'. 'Thoroughly penetrating' means thoroughly penetrating the principle of the three truths. Therefore the Mahāparinirvāṇa Sūtra says: 'Just like a person who well knows where a hidden treasure lies: he immediately takes a sharp hoe and digs straight down into the earth; boulders, sand, and gravel are passed straight through without difficulty; only when he reaches vajra can he pierce no further.' 'Boulders' are the delusions of views and thoughts. 'Sand' is the delusion of nescience [as numerous as] fine particles of dust and sand. 'Gravel' is the delusion of the entrenched ground of fundamental ignorance. 'Passing through' is precisely the meaning of piercing through. 'Reaching vajra' is thoroughly penetrating the principle of the one real truth, the buddha-nature.